Photocell amplifier



June 15, 1937. R. A. BRADEN 2,034,135 PHOTOCELL AMPLIFIER 1 Filed Feb. 1, ,1934 3 Sheets-Sheet 1 3,- .1. A is :rz'i' 1 I 9/ I 1. E 13 9 43 17 L L 4s Out t JAY INVENTOR:

Eerie AiBraden June 15, 1937. R. A. BRADEN 2,084,186

PHOTOCELL AMPLIFIER Filed Feb. 1, 1954 a Sheets-Sheet 2 INVENTOR H eneA.Br ad e n R. A. BRADEN Plio'rocELL AMPLIFIER June 15, 1937.

Fild Feb. 1, 1934 3 Sheets-SheeLS 1 Sec.

TIME

Sec

mm Rene A.Braden ATTOR EY 55 invention will appear second half cycle.

produces the greatest change Patented a... 15, 1937 PATENT. OFFICE 2,084,186 .rno'rocm minim Rene A. Braden,

Delaware Application February 1', 1934,

Coliintswood, N. 5., asaignor to Radio Corporation oi. America, a corporation of Serifl No. l 709,292

1 Claims. (01. 1719-111) My invention relates to amplifiers and particularly to amplifiers adapted for use with ,lightsensitive cells or the like.

One of. the objects of my invention is to pro vide an improved amplifier which may be operated by unrectifled alternating current.

'A further object of my invention is to provide an improved direct-coupled amplifier.

A further object of my invention is to provide an improved amplifier {or use in connection with light-sensitive devices or the like.

A still further object of my invention is to provide an improved amplifier ioroperating a direct-current relay.

In one embodiment of my inventiomI utilize a plurality of electric discharge devices, such as vacuum tubes, so connected to a source of alternating current that one of said devices opera ates on one half cycle and-alternate succeeding half cycles, while another of said devices operates on the intervening half cycles to the oppositepolarity. The input circuit of the second of said devices is supplied with amplified energyfrom' the output circuit of the first device by means of a condenser and resistance in said output circuit, this condenser being charged during the first one half cycle of operation, and remaining charged a certain amount during the In another embodiment of myinvention, *1 cperate a direct current relay by means of an elec-.- tric discharge device connected to an alternating current source. In a circuit of this type the usual mode of operation is to provide a grid bias voltage of such rent is practically zero. This is done because a relay operates most efllciently when there is no direct current flowing through it except during the period when it is actuated. 0n the other hand, the tube operates most emciently, (i. e., in plate current with a certain signal on the grid) when its grid bias is such that the plate currenthas a fairly,

large direct current component, because with such a bias the tube has greater mutual conductance than with a plate current to zero. Therefore, I adjust the electric discharge device for most eflicient operation and provide a rectifier circuit for balanc- 0 ing out the direct current component of the plate current which, otherwise, would flow through the relay. 7

Other objects, features and advantages of my from the following de- -energy during one-hall cycle of operation,

magnitude that the' plate cur-- bias which reduces thescription taken in connection with the accompanying drawings, in which Fig. 1 is a circuit diagram of one embodiment of. my invention,

Figs. 2, 3 and embodiments of my invention,

Fig. 5 is a circuit diagram of an embodiment of my invention adapted to operate a direct current relay, v

Figs. 6 and '7 are curves which are referred to inexplaining the operation of the circuit shown in Fig. 5, and

Fig. 8 shows a modification oi the tom 0! my invention shown in Fig. 5.

Referring to the embodiment otmy invention shown in Fig. l, the amplifier comprises an electric discharge device I such as a three-electrode vacuum tube having a cathode 3, a control grid 5 and an anode 1. Suitable voltages for the operation of the tube l are supplied from a voltage divider resistor 9 which is connected across any suitable source II of alternating current, such asan ordinary 60 cycle supply.

The cathode 3 is connected to the voltage divider 9 near one end' through a variable tap ll, while the anode I is connected to the voltage divider at the other end through a resistor l5 l1, whereby substantially the the source ll isapplied across the electrodes 8 and 1. A condenser i5 is connected across the plate resistor l5 for storing as will be explained hereinafter.

The input circuit of includes a light sensitive device such as a photoelectric cell 2| having a cathode 23 and an anode 25, the cathode 23 being connected to the control electrode 5 and the anode 25 beingconnected to a point on control grid 5 is connected to one end of the voltage divider 9 through a grid leak resistor 21 whereby the end section 29 of the voltage divider maintains the control electrode at a suitable negative potential during the half cycle of operation that the anode I is positive.

When the phase of the voltage from the source II is such as to make the right-hand end of the voltage divider 9 positive, a positive voltage is applied to the anode I of the discharge device I, a negative biasing voltage'is applied to the control electrode positive voltage is applied to the anode 25 of the photoelectric cell 2!. Under these conditions,

it which is proportional to the 4 are circuit diagrams of other the discharge device I the voltage divider 9. The.

5, and, at the same time, a I

intensity of the light and there will be a corresponding voltage drop across the grid leak resistor 21. The potential drop is such as'to make the cathode of the discharge device I more nega- 5 tive than normal with respect to its grid which is the equivalent of applying a more positive potential to the said grid, proportional to the light intensity. Accordingly, since the anode i is at a positive potential, there will be a flow of plate current having a value proportional to the light intensity. This flow-of plate current will charge up the condenser l8 by an amount depending upon the value of the plate current, the righthand terminal of the condenser l9 acquiring a positive polarity. During the next half of the cycle, the voltage across the condenser it is utilized to control a second electric discharge device indicated at iii. The resistance it] shunting condenser i ii is large enough so that the condenser will not be completely discharged during this one half cycle.

The device 3i may be a vacuum tube. similar to the first device and, as illustrated, includes a cathode 33, an anode 35 and a control electrode 31. The cathode 33 is connected through a variable tap 39 to the same end of the voltage divider 9 that the anode I of the electric discharge device is connected to. The anode 35 isconnected through. the load 4! to the opposite end of the voltage divider 9. Thus it will be seen that when the phase of the voltage from the source I! is such as tomake the first tube I operative, the second tube 3| is inoperative since im anode is at a negative potential. Like- 35 wise, when the phase of the voltage is such that the first tube is inoperative, the second tube 3| is operative.

The control grid 31 of the tube 3| to the plate end of the resistor l5. so that the output of the tube 3| is controlled by the voltage drop across the resistor l5. By connecting the cathode 33 to the voltage divider 9 at a point on one side of the variable tap H, a suitable biasing voltage may be applied to the control grid 3'1. In the diagram, the relation of the variis connected able taps H and 39 is such that when the second i tube 3| is operative, a slight negative bias is applied to its control grid 31 by a section 43' of the voltage divider 9. Referring now .to the operation of the circuit r the second half of the cycle, it will be apparent that during this half cycle the anode 35 of tube 3| is positive whereby a current may fiow through the load 4|, the value of the current depending upon the voltage applied to the control electrode 37. .We have seen that during the first half of the cyclethe condenser l9 was charged to some value depending upon the-intensity of the light striking the photoelectric cell 2|. The charge on the condenser l9, shunted by the resistor I 5, is such that, during the second half cycle, a negative potential is impressed upon the control electrode 31. 'I'herefore,if thelight striking the photoelectric cell 2| increases in in- 5 tensity, the value of current through the load 4| decreases.

When light striking the photoelectric cell 2| decreases, the. charge on condenser l9 leaks off through the resistor |5 until equilibrium is 7 reached at a new level. The plate current of tube 3| also readjusts itself to a higher value.

3| may be either increased or decreased by varying the intensity of the light striking the photoelectric cell.

In Fig. 2, the circuit of Fig. 1 i5 19M;:niodiwould be used current supplied from source 45 are preferably type in order that efiicient amplification of a comparatively high frequency alternating current may be obtained. Instead of a. 60 cycle supply, such as ordinarily in the circuit shown in Fig. 1, an alternating current source 45 preferably supplies currenthaving a frequency which is above audibilit cycles.

The output circuit of the discharge device 3| includes a low-pass filter 41 which has a cutoil frequency above the signal frequencies and below the frequency of the alternating current supplied by the source 45. Thus, the signals will appear in the output, while the high frequency will be filtered such as a frequency of 25,000

out.

While a photoelectric cell has been illustrated in the input circuit of the amplifier, it should be understood that a'signal voltage may be impressed upon the amplifier input circuit in any well known manner.

Referring to Fig. 3, the circuit of Fig. 1 is shown modified by the addition of two more electric discharge devices 49 and 5|. While only two additional discharge devices have been illusthe control grid 31 durin the half cycle the second device is in operation. This distinction, however, is not of any great importance as the character of the bias which is applied to the control grid 31 depends upon the particular type of tube used. The other distinguishing feature is that the output circuit of the tube 3| includes a resistor 55 shunted by a. condenser 51 which will device 48 may be controlled by the voltage across produced by the charged condenser 51.

The third electric discharge device 45, as illustrated, is a vacuum tube having a cathode 59, a control grid 6| and an anode 83, The cathode 59 is connected through a variable tap to an additional voltage divider section 51 provided for grid SI of the tube 49' is connected to the plate end of the resistor 55 whereby the condenser 51, if charged by tube 3|, will apply a negative potential to the control grid.

The fourth electric discharge device 5|, as illustrated, is a vacuum tube having a cathode l3, an'anode 15 .and a control grid 11. The cathode 13 is connected through a variable top 19 to a point near the same end of the voltage divider 8 to which the plate 63 of the preceding tube is connected. The anode 15 is connected through a load 8| to the opposite end ofthe voltage divider 9. The controlgrid 11 is, connected to the plate end of the resistor 69 whereby its poten-- tial may be controlled by the voltage to which the condenser II has been charged. It may be noted that the position of the variable tap 19 connecting the cathode 13 to the voltage divider, 9 issuch that a negative bias is applied to the control electrode 11 instead of a positive bias as in the case of the other tubes. The reason for this is that, in the particular circuit illustrated, I

tube which requires a will be understood from the foregoing description 25 given in connection with Fig. 1. It may be noted, however, that the signal is deiayeda certain amount in passing through 'the amplifier, the amount of the delay depending upon the number of tubes and the frequency of the alter- 30 nating current supply. That such a delay exists .will be made apparent by considering the fact a that a changein the charge on the first-condenser can'have no effect upon the charge of the second condenser until the second half cycle, and that 35 the change in the charge of the second condenser in turn can have no effect upon the charge of the third condenser until the third half cycle. Referring to the embodiment of my invention illustrated in Fig. 4, it comprises two electric discharge devices 93 and 85 connected in cascade for operatingv on one half cycle of an alternating .urrent and two other electric discharge devices 61 and 99 connected in cascade for operating on the succeeding half cycle of the alternating current. In the circuit illustrated, these devices are three-element vacuum tubes. They are provided withsuitable operating voltages by means 9i! a voltage divider 9I which is connected acrosswan alternating currentsource 93. The first discharge device 93 includes a cathode 95', a control grid 91 and an anode 99, the cathode 95 being connected through a variable the voltage divider 9I near the left-hand end and the anode 99 being connected through a coupling resistor I03 to the voltage divider 9| at a point near the middle.

A signal or control potential may be app ed to the input circuit of the first tube 93 in any suitable manner, as by means of a light sensitive 60' device I95which may be a photoelectriccell having a cathode IIi1and an anode I99. The anode I09 isconnected to a point on the'voltage divider 9| while the cathode I91 is connected directly to the control electrode 91 and to the left-hand end of the voltage divider 9 I through a grid leak resistor III. I

The second tube includes a'cathode H3, 3.

control grid. I I5.and an anode II1, the cathode I Isbeing connected to the lower end of the coupling resistor I93, and the control" electrode II being connected to its upper end. The anode II! is connected to the right-hand end of the voltage divider 9| through a resistor H9 and a variable 75 tap IZI, theresistor I i9 being shunted by a-concharge devices'will operate charge on the condenser I29 difiersfrom that shown in Fig.

tap IM to 18's 3 denser I29 provided for the purpose described in connection with the preceding figures.

It will be apparent that during the half cycle the anodes 99 and H1 are positive the two disin cascade to charge up the condenser I23 in accordance with the intensity of the light striking the photoelectric cell I95. During the succeeding half cycle, the will bias the grid of the tube 89 negatively and control the output of tube 91. 1 f

The vacuum tube 89 includes a cathode I25, a control grid I21 and an anode I29, the cathode- I25 being connected to the same end of the voltage divider 9I as that to which the anode II1 of the second discharge device 96 is connected. The anode I29 is connected through a coupling resistor ISI to the voltage divider at a point near the middle. The control electrode I2] is connected to the plate end of the resistor II9, whereby its potential is controlled in accordance with the discharge or the condenser The vacuum tube control grid I35 and an anode I91, the cathode I93 being connected to that end of the coupling resistor I9I which is connected to the voltage divider, and .the

anode I31 being connected through a load voltage divider 9I. The control electrode I35 is connected to the plate end of the coupling resistor I3I whereby the vacuum tube 81 is connectedin cascade with the preceding tube 89.

It will be noted that the circuit shown in Fig. 4 1 in that only about half the voltage from the alternating current source 93 is impressed across the cathode and anode of each discharge device and in that a plurality of discharge devices operate as a cascade amplifier during each .half cycle. Referring to Figure 5, there is shown the circult diagram of a photoelectric cell amplifier designed for operating a direct current relay. This circuit is designed to overcome two apparently conflicting requirements for eflicient operationoi the amplifier, one requirement being that the amplifier tube be so biased that it has high mutual conductance and the other re-' quirementbeing that there shall be no flow of direct current through the relay until the relay is to operate. These requirements are conflicting because a bias which will give the amplifier tube 'a'high mutual conductance will cause a flow of direct current in-its plate circuit. I have found that by employing a condenser and rectifier combinationit' is possible to' prevent a.

flow of direct current through the relay, exc'epting during the period it is to operate, and at the same time to bias the amplifier tube for high mutual conductance.

-Referring to th circuit diagram, the appara tus comprises an amplifier tube I5I which may be any suitable form of electric discharge def vice, such as either a three element or a screen grid vacuum tube having a photoelectric cell 91 includes a cathode I33, a"

I39 to the left-hand end of the I59 connected to its input circuit. In the drawings, there is illustrated a three element vacuum tube having a cathode I55, a control electrode I51 and a plate electrode I59. Ari alternating current operating potential is supplied to the vacuum, tube IISI from any which preferably has a voltage divider I63 connected thereacross. The voltage divider may be eithera tapped inductance coilor a tapped resistor, as illustrated.

suitable source IIiI rectifier HI The cathode I of the amplifier tube is connected to a point on the voltage divider I83 intermediate its ends, while the control electrode I51 is connected throughra resistor iSlto a point near one end of the voltage divider.

The photoelectric cell "53 has a cathode I61 The direct current relay I73, which is to be operated in response-to a change in light of the photoelectric cell I53, consists of a relay winding H5 and an armature Ill. The winding "5 is connected in the plate circuit of the amplifier tube I55, one end of the winding being connected to the plate electrode I 59 and the other end of the winding being connected to one end of the voltage divider lol It will be apparent that, with the circuit as described above, there would be a flow of pulsating current through the relay winding 115. As is well knovn, such a current has a direct cur rent component.

1E prevent such a direct current component from appearing in the relay winding I'M by means of a condenser W9 and a rectifier Mill. The condenser llil is connected across the relay winding H5 whereby it will become charged during the half cycle that plate current flows in the amplifier tube not.

Une terminal of the rectifier Nil is connected through a variable tap 9533 to theivoltage divider l while the other terminal of the rectifier till is connected to the upper terminal of the condenser we through variable resistor The rectifier ltii is connected in such a clirection that current flows through it in direction indicated by the error].

With given values of inrluctsuoce and resistance for the relay coil i'lii, the condenser H9 is made large enough to maintain fairly high value of current flow tli'rou the winding during half cycle that electrode 553 is negative and the c is discharging. In other words, the constant or" the circuit comprising the condenser lit) and the relay coil llil is greater than ti th of a second in the case where alternating current supply has a frequency of 50 cycles per second. It may be noted that, the frequency of the supply source employed, the inductive reactance of the coil H5 is small compared with its resistance.

Under the above described conditions, if the were removed from the circuit, the current flow through the relay winding H5 would be as indicated by the curve in Figure 6. An inspection of this curve shows that during the half cycle that the plate electrode is positive the condenser H9 is given a certain charge, plate current at the same timeilowing through the relay winding H5. During the next half cycle the condenser I19 discharges a certain amount through the relay coil I15 but it does not have time to discharge completely before the next positive half cycle appears. Thus the charge on the condenser H9 gradually increases and the current flowing through the relay coil 115 has a rather large direct current component,

as indicated by the curve.

By adding the rectifier viously described,

to the circuit, as prethe curve or the current flow through the relay winding I75 is changed to have the characteristic shown inFigure 7. with the rectifier in the circuit, the condenser "9 Charges the light intensity. By utilizing up during the positive halt cycle, as described above, and discharges through the relay winding H5 and the rectifier l8! during the negative half cycle. The difference in the circuit operation is that now, during the negative half cycle, the voltage drop across the voltage divider portion i81 causes a flow of current through the rectifier ill! in such a direction as to aid the discharging of the condenser H9 and to charge it a certain amount in the opposite direction, this charge being indicated by that portion of the curve appearing below the horizontal line. Thus, the circuit may be so adjusted that for a given light intensity on the photoelectric cell I53, the condenser ill! will be discharged a sufficient amount to prevent it from acquiring a greater charge with each succeeding cycle. It will be apparent from the curve 01' Fig. 7 that the current now blowing through the relay winding contains substantially no direct current component.

The alternating current represented by the curve in Fig. '7 either is maintained at a low value compared with the direct current which is to operate the relay, or it is filtered out entirely by means of filter connected as shown in Figure 8. ll so u. filter is provided, it is preferably or the in type comprising a series cell 185 and shunt condensers HM and having a cut-oil frequency below the frequency of the supply current.

' or may be adjusted for the above The a described condition of no direct current coropoc t in "clay winding under the condition. of

yen intensity the photocircuit that with no light "ootoelectric cell tilt the direct curat through the relay winding iii d. With this adjustment, the instant znpliiier tube lbi is decreased, since ode till is made less negative, and er llil acquires a greater charge than ercby the circuit is unbalanced and component in the relay 'JZB to operate the relay.

understood that ii? the circuit is bal condition of a given. light intensity on the otoelectric cell the relay may be operated by either a decrease or an increase in a pole. -ized relay, it may be made to operatedn one direction when the light intensity increases and in the opposite direction when the light intensity decreases.

Various other modifications may be made in my invention without departing from the spirit and scope thereof and I desire, therefore that only such limitations shall be placed thereon as ahead are necessitated by the prior art and set forth in the appended claims.

I claim as my invention:

1. In combination, a plurality of electric discharge devices, each of said devices having an input circuit and an output circuit, a source of power for supplying alternating current thereto, means for so connecting said devices to said source that one of said devices is operative on only one half cycle of said current while another oi said devices is operative on only the succeeding halt cycle, a condenser in the output circuit 0! said one device, and a resistor connected across said condenser, the input circuit of said other device being connected across at least a portion of said resistor.

practice, the usual adjustment the photoelectric cell, the imperl- 2. In combination, a plurality oi electric discharge devices, a source oi power for supplying alternating current thereto, means for so connecting said devices to said source that one of said devices is operative on only one half cycle of said current while another of said devices is i operative on only the succeeding halt cycle,

means for storing at least a portion of the output energy of said first devioe'during said one halI cycle, and means for controlling said second device in accordance with said stored energy during said succeeding halt cycle.

3. In combination, a plurality of electric discharge devices, each oi! said "devices having a cathode, an anode, and a control electrode, a source of alternating current, the cathode and anode of one or said devices being connectedv across said source, the cathode and anode of another of said devices being oppositely connected across said source whereby said two devices are operative only on alternate halt cycles of said current, means connected between the anode of said one. device and said source for storing elecdivider, the anode of said one device being connected to the other end of said voltage divider, the cathode oi! another of said devices being connected to said other end of said voltage divider and its anode being connected tosaid one end of said voltage divider whereby said two devices are rendered operative on opposite halt cycles, a condenser connected in the anode circuit of said first device, and means for controlling the potential of the control electrode of said second device in accordance with the charge on said condenser.

5. In combination, charge devices, means for connecting said devices to a power source of alternating potential, means for rendering one of saiddevices operative during one half-cycle and means in circuit with each of said devices for controlling the operation of another 01 said devices during a subsequent halt-cycle in accordance with the operation of the first mentioned device during the first halfcycle.

a plurality of electric dis- 6. Apparatus according to claim 5 character-- ized in that a photo-electric cell is included in the input circuit of said one device.

7. An amplifier according to claim 2 characterized in that said alternating current has a frequency which is highcompared with the irequency oi the signal to be amplified and further characterized in that means is provided for filtering out said alternating current from the amplifier output. l i

, RENE A. BRADEN. 

